How Is DNA Sequenced

Finally, we must ask one last question about the genetic code Is the code universal That is, is it the same for all organisms Every bit of experimental evidence available today from the study of viruses, bacteria, and higher animals, including humans, indicates that the code is universal. Furthermore, the fact that it is the same for all these organisms means that it has been the same over millions of years of evolution. 

During transcription, a portion of mRNA is synthesized with the following base sequence  

During transcription, mRNA is synthesized from a DNA strand beginning from the 3 end of the template. The DNA strand must be the complement of the newly synthesized mRNA strand. 

Note that the codon UGA codes for termination of the growing polypeptide chain therefore, the sequence given in this problem codes for a pentapeptide only. 

The following section of DNA codes for oxytocin, a polypeptide hormone  

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Explain how a DNA sequence (enhancer sequence) located 5,000 bp from a gene transcription start site can stimulate transcription even if its orientation is reversed. 

A genetic mutation is a permanent, heritable change in the DNA nucleotide sequence of a gene. Depending on how the DNA sequence is modified. 

Whether a gene is positioned in active or inactive chromatin certainly also plays a large role in whether or not transcription can occur. The various elements which define active chromatin (sensitivity and hypersensitivity to nucleases, presence of HMG proteins, modifications of both histone and nonhistone chromosomal proteins, DNA methylation) have recently been reviewed (Weisbrod, 1982 Razin and Riggs, 1980). With a few exceptions, there is no clear idea how the DNA sequences and proteins which are known to modulate transcription relate to the formation of active chromatin. Such a discussion must therefore be deferred to a later date. 

Sequences farther upstream from the start site determine how frequently the transcription event occurs. Mutations in these regions reduce the frequency of transcriptional starts tenfold to twentyfold. Typical of these DNA elements are the GC and CAAT boxes, so named because of the DNA sequences involved. As illustrated in Figure 37—7, each of these boxes binds a protein, Spl in the case of the GC box and CTF (or C/EPB,NF1,NFY) by the CAAT box both bind through their distinct DNA binding domains (DBDs). The frequency of transcription initiation is a consequence of these protein-DNA interactions and complex interactions between particular domains of the transcription factors (distinct from the DBD domains—so-called activation domains ADs) of these proteins and the rest of the transcription machinery (RNA polymerase II and the basal factors TFIIA, B, D, E, F). (See... 

A developing application of DNA technology uses a DNA chip that contains many small segments of bases of known sequence. Such DNA chips are being used to attack cancers. Cancers occur when defective genes cause cells to divide uncontrollably, but usually the process of protein synthesis also is modified. Different types of cancer result in different modifications to protein synthesis, depending on how the DNA... 

The discovery of the base-paired, double-helical structure of deoxyribonucleic acid (DNA) provides the theoretic framework for determining how the information coded into DNA sequences is replicated and how these sequences direct the synthesis of ribonucleic acid (RNA) and proteins. Already clinical medicine has taken advantage of many of these discoveries, and the future promises much more. For example, the biochemistry of the nucleic acids is central to an understanding of virus-induced diseases, the immune re-sponse, the mechanism of action of drugs and antibiotics, and the spectrum of inherited diseases. 

The Xenopus transcription factor IIIA not only acts as an essential RNA polymerase transcription factor for the expression of the 5S rRNA gene, it also binds to the 5S rRNA to form a 7S ribonucleoprotein particle that stabilizes the RNA until it is required for ribosome assembly and facilitates nuclear export of the 5S rRNA. Indeed, it was originally shown to be the protein component associated with 5S rRNA in the 7S particle in Xenopus oocytes before it was recognized as a transcription factor. How, we may ask, can this protein not only recognize specific DNA sequences in the 5S rRNA gene upstream region, but also recognize different, but equally specific, sequences in 5S rRNA ... 

As deduced from the DNA sequence of the gene, AMDase contains four cysteine residues. Since a-halocarboxylic acids are generally active alkylating agents there is a possibility that a-bromophenylacetic acid reacts with several cysteine residues of the enzyme. Therefore, we tried to clarify how many cysteine residues react with this inhibitor. It is well established that when p-chloromercuri-benzoate (PCMB) binds to a cysteine residue, the absorbance at 255 nm increases due to the formation of an aryl-Hg-S bond. Thus it is possible to estimate the number of free S-H residues of the enzyme by titration with PCMB solution (Fig. 6). When the native enzyme had reacted with PCMB, the absorbance at 255 nm increased by 0.025. On the other hand, when PCMB solution was added to the enzyme solution after the enzyme was incubated with a-bromophenyl-... 

Above I noted that DNA sequences of the genomes of man and chimps are about 99% the same. Those sequences for the genomes of man and mouse are about 98.7% the same. What is the meaning for these apparently very modest differences at the level of the essential molecules of life In fact, the commonly cited figure of a 1% difference between humanness and chimpness may be more misleading than useful. It does serve to indicate just how closely we really are related. 

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